In recent years, electronic watches provided with a solar cell unit have been proposed, in which electric power generated by the solar cell unit is charged to a condenser or a secondary battery and the generated power is utilized to drive these watches.
Such an electronic watch uses a solar cell unit as a power source so that no replacement of a cell is required. This technology has met a recent enhanced ecological demand and is hence rapidly becoming widespread throughout various fields.
Here, In the case of mounting a solar cell unit in an extremely small device such as a watch, it is necessary to supply with certainty sufficient light to a solar cell. Because of this, it is desirable that the solar cell unit be disposed at a dial portion possessing the largest area in the watch.
While, in simple analog type watches which display the time using three or two hands, the design of a dial is of the most importance. It is therefore undesirable for the design of the watch with a solar cell having a deep violet color, if such solar cell appears on a dial portion.
For the above reason, in conventional analog type watches, a solar cell unit is disposed on the dial and a light transmittable material with a white or another color is arranged on the solar cell to avoid direct exposure of the solar cell and thereby to improve the design of the watch while sufficient light is supplied to the solar cell.
At present, extremely simple and usual watches such as the aforementioned analog type watches which display the time using three or two hands are widely received in the market. On the other hand, unusual watches such as watches adopting a digital display using a liquid crystal cell or the like to display the time are also favorably received.
Such a digital display watch, however, has various structural problems when using a solar cell unit as a power source.
The analog type watch has no problem with its functions if a solar cell unit is disposed on the dial. Also, the design problem can be solved by arranging the light transmittable material with various colors on the solar cell.
However, in the digital display watches, when a solar cell unit is mounted on a digital display, the solar cell covers the digital display and hence the display is not viewed. It is therefore impossible to dispose a solar cell unit over the entire display in the same manner as in the analog watches.
If a solar cell unit is disposed below the digital display, there is the problem that light is not supplied to the solar cell. More concretely, a liquid crystal display material constituting a digital display is generally provided with a reflecting plate at the lowest side thereof to easily distinguish characters and the like displayed by a liquid crystal cell. If the solar cell unit is disposed below such a digital display in the above manner, incident light from the outside is reflected by the reflecting plate so that no light is supplied to the solar cell. It is therefore impossible to dispose the solar cell unit below the liquid display material in the conventional digital display electronic watches.
As a structure provided with a solar cell unit in the digital display watch, to date there has only been a structure such as disclosed, for example, in Japanese Patent Application Laid-open No. 287427/1990 in which a solar cell unit is disposed on a digital display at a position which never overlaps a liquid crystal cell. Such an arrangement is general at present.
However, in the structure in which the solar cell unit is disposed in such a manner as disclosed in Japanese Patent Application Laid-open No. 287427/1990, almost all parts of the watch surface on which the digital display is arranged are covered with the solar cell. Hence, the area for the digital display for displaying the essential time and the like is considerably narrowed, presenting a fatal problem for a watch inasmuch as the time and the like can be seen only with difficulty.
As outlined above, a structure for mounting a solar cell unit has important and serious problems in the case where it is intended to use the solar cell unit in digital display watches provided with a digital display composed of a liquid crystal and the like.
Incidentally, in recent years watches such as a wrist watch have been developed in which a light transmitting liquid crystal cell is used for a display to indicate the time, thereby providing a watch with an interesting effect.
Though such a watch itself has an interesting effect, it can never be a solar cell product which can meet an ecological demand since it uses a normal battery as a power source. Also, no technology in which a solar cell is mounted in such a watch provided with a light transmitting liquid crystal cell and is allowed to function efficiently as a watch material has as yet been proposed or realized.
Accordingly, the present invention has been achieved in view of this situation and has an object of providing a electronic watch equipped with a solar cell provided with a digital display which has a large area for supplying light to a solar cell to generate sufficient power and which allows the digital display to occupy a large area and to be easily seen, ensuring that the digital display has a large enough area to indicate multifunctional display portions, while at the same time it is an ecological watch in which a solar cell unit is mounted and characters and the like can be easily seen, bringing about a high product value.